[patch 5/8] x86/entry/common: Provide trace/kprobe safe exit to user space functions

Thomas Gleixner
2020-02-25T23:30:41Z

Split prepare_enter_to_user_mode() and mark it notrace/noprobe so the irq
flags tracing on return can be put into it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/entry/common.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -196,7 +196,7 @@ static void exit_to_usermode_loop(struct
}

/* Called with IRQs disabled. */
-__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
+static inline void __prepare_exit_to_usermode(struct pt_regs *regs)
{
struct thread_info *ti = current_thread_info();
u32 cached_flags;
@@ -241,6 +241,12 @@ static void exit_to_usermode_loop(struct
mds_user_clear_cpu_buffers();
}

+__visible inline notrace void prepare_exit_to_usermode(struct pt_regs *regs)
+{
+ __prepare_exit_to_usermode(regs);
+}
+NOKPROBE_SYMBOL(prepare_exit_to_usermode);
+
#define SYSCALL_EXIT_WORK_FLAGS \
(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
@@ -271,7 +277,7 @@ static void syscall_slow_exit_work(struc
* Called with IRQs on and fully valid regs. Returns with IRQs off in a
* state such that we can immediately switch to user mode.
*/
-__visible inline void syscall_return_slowpath(struct pt_regs *regs)
+__visible inline notrace void syscall_return_slowpath(struct pt_regs *regs)
{
struct thread_info *ti = current_thread_info();
u32 cached_flags = READ_ONCE(ti->flags);
@@ -292,8 +298,9 @@ static void syscall_slow_exit_work(struc
syscall_slow_exit_work(regs, cached_flags);

local_irq_disable();
- prepare_exit_to_usermode(regs);
+ __prepare_exit_to_usermode(regs);
}
+NOKPROBE_SYMBOL(syscall_return_slowpath);

#ifdef CONFIG_X86_64
static __always_inline
@@ -417,7 +424,7 @@ static __always_inline long do_fast_sysc
/* User code screwed up. */
local_irq_disable();
regs->ax = -EFAULT;
- prepare_exit_to_usermode(regs);
+ __prepare_exit_to_usermode(regs);
return 0; /* Keep it simple: use IRET. */
}